OAKLAND — Oakland police confirmed Saturday it was the fifth agency in the Bay Area to receive an envelope filled with white powder in the mail, sparking investigations from hazardous materials crews and the FBI.

The unidentified substance, determined not to be hazardous, was discovered sometime early Friday evening, Oakland police said.

Authorities did not say whether they believe the deliveries are connected. At least four of the police agencies plan to conduct a joint criminal investigation to find out who mailed the substances to them.

On Saturday, Oakland police had not announced its plans.

The substance in three other envelopes delivered Friday to police in Hayward, San Leandro and Berkeley was also not hazardous, officials said. A fourth envelope delivered Friday to the Union City Police Department was given over to the U.S. Postal Service and the FBI for more investigation, police Cmdr. Kelly Musgrave said.

Test results were not available Saturday.

No other police departments reported receiving similar envelopes, but agencies around the Bay Area were alerted to it, Alameda County fire spokeswoman Aisha Knowles said. The substance delivered to San Leandro was baking flour, Lt. Greg Lemmon said, but authorities did not identify the substance found at the other stations.